1. Field of the Invention
This invention relates to a sewing machine, and more particularly, to a needle receiving assembly for a sewing machine.
2. Description of the Related Art
A full-turn shuttle hook and a half-turn shuttle hook are two examples of available shuttle bodies in sewing machines. In one type of the half-turn shuttle hook (hereinafter referred to as a "DBS shuttle hook"), the needle comes between an upper thread loop and the bobbin. The needle drop position is between the bobbin thread lead-out point of the bobbin and the beak of the shuttle body. In another type of the half-turn shuttle hook (hereinafter referred to as a "DPS shuttle hook"), the upper thread loop comes between the needle and the bobbin. Here, the beak of the shuttle body is between the needle drop position and the bobbin thread lead-out point of the bobbin.
A sewing machine incorporating a DBS shuttle hook forms perfect stitches in a forward feeding direction in which a fabric is fed in a right-to-left direction as viewed from the operator, and forms hitch stitches in a reverse feeding operation (in which a fabric is fed in a left-to-right direction as viewed from the operator). Hence, the sewing machine of this type is extensively employed for lock stitching.
In general, in lock stitching, perfect stitching should be employed to form straight stitches from the view point of the quality of stitches, and in order to eliminate the difficulty of a thread getting loose at both ends of a line of stitches, the latter should be ended by hitch stitching. In order to meet these requirements, a DBS shuttle hook is employed. However, a sewing machine having a DBS shuttle hook is not suitable for omnidirectional stitching.
A sewing machine incorporating a DPS shuttle hook is also known in the art (see, e.g., Japanese Patent No. 99353). This type of sewing machine is capable of forming perfect stitches in both the forward feeding direction and the reverse feeding direction and is thus suitable for omnidirectional stitching. However, this type of sewing machine is not popularly employed in the art yet. Additionally, it should be noted that the DPS shuttle hook responds well to the variation in thickness of a fabric, and is thus suitable for sewing a heavy weight fabric and for use with a thread large in yarn number count.
FIG. 6 shows a conventional bobbin case 100 used with a half-turn shuttle. As shown in FIG. 6, the bobbin case 100 has an engaging member 101, in which a thread hole 102 is formed. A bobbin thread 104 supplied from a bobbin 103 accommodated in the bobbin case 100 is passed through the thread hole 102 of the horn 101 of the bobbin case 100. The bobbin case is set in the sewing machine (not shown) such that it faces forward so that it is conveniently handled by an operator when it is set in or removed from the sewing machine.
The direction of rotation of the shuttle body should be determined so that the upper thread on the needle side is twistable because a sewing thread for a sewing machine is fundamentally of Z-twist. Thus, in the case of a DBS shuttle hook, the direction of rotation of the shuttle body is clockwise as viewed from the operator side. However, in the case of a DPS shuttle hook, the direction of rotation of the shuttle body is counterclockwise.
FIG. 7 shows a conventional shuttle race body 121 and a conventional shuttle race ring 125. The shuttle race body 121 has a recess 122 which is opened upwardly and in its joining surface which is brought into contact with the shuttle race ring 125. The shuttle race ring 125 has a needle receiving section (or rear loop receiving section) 126 in its joining surface which is brought into contact with the joining surface of the shuttle race body 121 in such a manner that the needle receiving section 126 confronts with the recess 122 of the shuttle race body 121. In FIG. 7, reference numeral 127 designates an engaging groove with which the horn 101 (FIG. 6) is engaged.
FIG. 8 shows the needle receiving section (or rear loop receiving section) 126 with the shuttle race ring 125 coupled to the shuttle race body 121. As shown in FIG. 9, when a DBS shuttle hook is employed, the needle receiving section 126 of the shuttle race ring 125 is capable of regulating a rear limb 114r on one side of the needle 113 and securing a front limb 114R on the other side. The front limb 114R is scooped up with the beak 112 of the DBS shuttle hook.
A sewing machine incorporating a DBS shuttle hook and a sewing machine incorporating a DPS shuttle hook will now be compared with reference to FIGS. 10(a) and 10(b).
In FIG. 10(a), reference numeral 111 designates the DBS shuttle hook; 112, the beak of the DPS shuttle hook 111; 113, the needle; 114, the upper thread; and R, the upper thread loop. In FIG. 10(b), reference numeral 115 designates the DPS shuttle hook; and 116, the beak of the DPS shuttle hook 115.
In the case where the DBS shuttle hook 111 is employed, the distance (1) between the needle drop point and the bobbin thread lead-out point is as shown in FIG. 10(a). In the case where the DPS shuttle hook 115 is employed, the distance (2) between the needle drop point and the bobbin thread lead-out point is as shown in FIG. 10(b). As shown in FIGS. 10(a) and 10(b), the distance (2) is larger than the distance (1).
In the case where the DPS shuttle hook 115 is employed, the distance (2) between the needle drop point and the bobbin thread lead-out point must be shifted laterally as much as (the width of the lace of the shuttle body+.alpha. (alpha)) when compared with the distance (1) between the needle drop point and the bobbin thread lead-out point in the case where the DBS shuttle hook 11 is employed.
In the case where the DPS shuttle hook 115 is employed, the beak 116 comes between the needle receiving groove (or rear loop receiving section) 126 of the shuttle race ring 125, and the loop R of the upper thread 114 is positioned on the side of the needle receiving section 126. Hence, in this case, unlike the case where the DBS shuttle hook is employed, the needle receiving groove 126 cannot regulate the rear limb.
However, if, in the case where the DPS shuttle hook 115 is employed, the rear limb cannot be regulated as was described above, then it is impossible to obtain the front limb sufficiently, and accordingly it may be impossible to scoop it up with the beak.
Heretofore, the shuttle race ring 125 has been integral with the needle receiving section (or rear loop receiving section) 126. Hence, it was impossible to adjust the position of the needle receiving section 126. This is another problem accompanying the employment of the DPS shuttle hook 115.